<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
      width: 300px;
      height: 300px;
      background-color: skyblue;

      /* 1、单个属性 */
      /* border-width: 10px;
      border-style: solid;
      border-color: red; */

      /* 2、连写形式 */
      /* border: 10px solid blue; */
      /* border: 10px dotted orange; */

      /* 3、单方向设置 */
      /* border-top: 10px solid red; */
      border-bottom: 10px solid orange;
    }
  </style>
</head>
<body>
  <div></div>
</body>
</html>